Venom immunotherapy for the prevention of Hymenoptera sting-induced anaphylaxis in patients with prior histories of anaphylactic reactions is remarkably effective. For therapy to remain effective, it must be continued indefinitely. Since the natural (untreated) course of insect-sting hypersensitivity is unknown and since the long-term side effects and toxicity of such treatment are also unknown, the proposed research will be aimed at determining whether individuals with milder reactions may be safely observed without treatment; whether in vivo (skin testing) and in vitro (IgG and IgE determinations) studies can predict which individuals will require treatment; and whether venom-treated individuals have a higher incidence of abnormal physical or laboratory findings than comparable untreated individuals.